1. Field of the Invention
The invention relates to a method of manufacturing a liquid crystal display device, and in particular, a method of manufacturing a liquid crystal display device having reduced stitch spots.
2. Description of the Related Art
A cathode ray tube (CRT) has been widely used as an information display device. The CRT has many drawbacks such as a large size and low mobility. A liquid crystal display device has advantages of a compact size, a lightweight and low power consumption. Recently, the liquid crystal display device is frequently used with information processing apparatus requiring a display device.
The liquid crystal display device is a display device using modulation of light generated by a liquid crystal cell. A predetermined molecule arrangement of a liquid crystal is converted to other molecule arrangement by applying a voltage to the liquid crystal cell. The light is emitted through the converted molecule arrangement. The liquid crystal display device displays images by converting optical characteristics of the liquid crystal cell such as birefringence, an optimal rotary power, a dichroism and a light scattering character to visual variations.
The liquid crystal display device is manufactured by forming a gate line, a data line and a TFT on an array plate. Color filter layers such as R, G and B color filters are formed on a color filter plate and the color filter plate is aligned on a glass plate to face the array plate. The array plate and the glass plate are attached to each other with the liquid crystal interposed therebetween.
The array plate and the color filter plate are formed by sequentially performing a mask process. In the mask process, an insulating layer or a metal layer is deposited on an entire surface of the glass plate with a chemical vapor deposition (CVD) or a sputtering method. After depositing, a surface of the depositing layer formed on the plate is cleaned and a photo resist layer is coated. After coating, a target pattern is formed by using an exposure process and a developing process using a mask.
The depositing layer is etched by using the patterned photo resist layer to form a target pattern and the pattern photo resist layer is eliminated. By eliminating the pattern photo resist layer, a single mask process is completed.
FIGS. 1(a) and 1(b) illustrate an exposure method used in a manufacturing method of a liquid crystal display device according to a related art. As shown in FIG. 1(a), four active array plates are formed on a single glass plate. Four active areas corresponding to the four liquid crystal panels are formed simultaneously on the glass plate. After forming the four active areas, a cell process is performed for cutting the glass plate in a unit of a single active area.
The process forming the four active areas on the glass plate includes a first mask process of forming a gate line and a gate electrode on each of the four active areas, a second mask process of forming a channel layer, a third mask process of forming a source/drain electrode, a fourth mask process of forming a contact hole on a passivation layer, and a fifth mask process of forming a pixel electrode.
An exposure process is performed in each mask process. When the first mask process is performed, a metal layer is deposited on the glass plate and a photo-resist layer is coated on the metal layer. After coating, the exposure process is performed according to a mask pattern. The exposure process is performed four times on each active area sequentially.
In the exposure process, a single active area may be completely exposed with one time exposure process. As shown in FIG. 1(b), one or two active areas are formed on a glass plate in case of a large liquid crystal display device. In this case, a mask process is progressed by performing a plurality of exposure processes on each active area. The plurality of exposure processes is performed when each mask process is performed for forming an active area.
Manufacturing cost may increases in proportion to a size of an exposing lens. Although a size of a liquid crystal display device is small, a partitioned exposure process is performed to reduce the manufacturing cost. The size of the exposing lens may be reduced with the partitioned exposure process. The number of partitioned exposing areas may be 2, 3 or 4.
As described above, the partitioned exposure process completes a single mask process by performing a plurality of partitioned exposures on a single active area. On the other hand, a concentrated exposure process completes the single mask process by exposing an entire active area with one time exposure. The partitioned exposure process and the concentrated exposure process are selectively used in the manufacturing process of the liquid crystal display device. The partitioned exposure process may include one exposure process that generates overlapped exposing areas and the other exposure process that does not generate the overlapped exposing areas.
FIG. 2 shows overlapped exposing areas when an overlapping partitioned exposure process is performed. The overlapping partitioned exposure process produces overlapping exposing areas. As shown in FIG. 2, the overlapping partitioned exposure process performs a first exposure process to expose an active area within a predetermined width from a left edge of an active area formed on a glass plate. By the first exposure, a first exposing area is formed on the active area. After performing the first exposure, a second exposure is performed on an adjacent active area to form a second exposing area. When the second exposure is in progress, an overlapped exposing area is formed at the boundary area between the first exposing area and the second exposing area. Two exposing areas are illustrated in FIG. 2, but three or more exposing areas are possible. A size of a partitioned exposing area may increase with the overlapped area.
The overlapping partitioned exposure process is performed for forming a pixel electrode during a liquid crystal display device manufacturing process. The overlapping partitioned exposure process generates overlapped exposing areas, which may be used to secure a pattern margin.
FIG. 3 shows a exposing method for use with a liquid crystal display device manufacturing process according to a related art. As shown in FIG. 3, a partitioned exposure process is performed to manufacture a liquid crystal display device. The partitioned exposure process does not produce overlapping exposing areas.
Three partitioned exposures are performed for a liquid crystal panel in a first mask process of forming a gate line. A first exposure, a second exposure and a third exposure are orderly performed from a left edge of an active area for exposing an entire active area. After completing the partitioned exposure process, the gate line is formed by developing and patterning a photo resistor and performing an etching process.
After forming the gate line according to the first mask process as described above, three partitioned exposures are performed with a second mask process. The second mask process is performed with a developing process and an etching process for forming an active layer. After forming the active layer, a third mask process of forming a data line and a source/drain layer and a fourth mask process of forming a contact hole on a passivation layer are performed according to the partitioned exposure process. After completing the fourth mask process of forming a contact hole on the passivation layer, a fifth mask process is performed to form a pixel electrode by depositing an indium tin oxide (ITO) transparent metal layer. A pixel layer is formed by the fifth mask process.
In the fifth mask process of forming the pixel electrode, four partitioned exposures are performed. The overlapping partitioned exposure process (LEGO Pattern) is performed to generate an overlapped exposing area at the boundary between neighboring partitioned areas to obtain a pattern margin.
As described above, the partitioned exposure process is performed during the first to fourth mask processes. The overlapping partitioned exposure process is performed in the fifth mask process to generate an overlapped exposing area.
The overlapping partitioned exposure process is performed only in the mask process of forming the pixel electrode and is not performed in other mask processes. An overlayer change (pattern difference) is generated between a pattern of a pixel electrode formed on a layer where the overlapping partitioned exposure process is performed and a pattern formed on a layer where the overlapping partitioned exposure process in not performed. A stitch spot inferiority may be generated due to the pattern difference. Since the partitioned exposures are performed in the first, second, third and fourth mask processes and the overlapping partitioned exposures are performed in the fifth mask process, a large pattern variation may develop between a pattern formed on the first layer to the fourth layer and a pattern formed on the fifth layer. Accordingly, there is a need of a method of manufacturing a liquid crystal display device that substantially obviates drawbacks of the related art.